1. Field of the Invention:
This invention relates to an imaging apparatus having a solid state imaging device.
2. Related Art Statement:
Recently there is extensively used an endoscope apparatus whereby, by inserting an elongate insertable part into a body cavity, the body cavity interior can be observed or, as required, by using a treating instrument, a therapeutic treatment can be made or, by inserting the above mentioned insertable part into a pipe hole, the interior of the pipe hole can be observed.
Among such endoscope apparatus, there are an optical endoscope in which, for example, a fiber bundle is used as a transmitting optical system and an electronic endoscope in which such solid state imaging device as a charge coupled device (CCD) is used as an imaging apparatus.
This electronic endoscope has advantages that it is higher in the resolution and is easier to record, reproduce, magnify and compare images than the optical endoscope.
As disclosed in the publication for example, of Japanese Patent Application Laid Open No. 2721807/1988, the above mentioned solid state imaging device is fixed in an image forming position by an objective lens so that an optical image of an observed part formed by this objective lens may be photoelectrically converted by the above mentioned solid state imaging device and may be amplified by an amplifying circuit provided on a circuit substrate. This amplified signal is input into an image signal processing circuit within a video processor through a signal cable connected to the circuit substrate and is then output in a television monitor so that the image of the observed part may be observed through this television monitor.
However, the above mentioned amplifying circuit will generate heat during the operation. A regulator is arranged generally on the above mentioned circuit substrate and will also generate heat during the operation. When the heat of such heat generating parts as these amplifying circuit and regulator is transmitted to the solid state imaging device, the temperature of the solid state imaging device will rise to be above the standard operating temperature, heat noises will be generated, the image displayed in the television monitor will deteriorate and the durability of the solid state imaging device will also reduce.
For example, whereas the standard operating temperature of the above mentioned solid state imaging device is about 55.degree. C., the using limit operating temperature of an amplifying IC which is an example of an amplifying circuit is above 70.degree. C. and thus the solid state imaging device is lower in the heat capacity. In an experiment in case the amplifying circuit was supposed to be arranged adjacently to the solid state imaging device, the temperature of the solid state imaging device rose to about 58.degree. C.
In order to cope with this, it may be considered to arrange the heat generating part in such part separated sufficiently from the solid state imaging device as on the hand base side or in the course of the above mentioned insertable part so that it may be difficult for the heat of the heat generating part to be transmitted to the solid state imaging device. However, when such heat generating part as the amplifying circuit and the solid state imaging device are separated from each other, the distance for transmitting signals will become longer, the outside turbulent noises will be more likely to come in and the apparatus will be likely to become larger.
As disclosed, for example, in U.S. Pat. No. 4,491,865, in the above mentioned electronic endoscope, a solid state imaging device is provided on a substrate, a signal line to be connected is fixed with a resin or the like on the back side of this substrate and the whole is sealed within a housing to mostly prevent fogging from being caused by a moisture mixed in and reinforce the strength of the housing.
Besides the above mentioned formation example, the housing is provided within it with a solid state imaging device, a driving circuit driving this solid state imaging device and an output buffer outputting a video signal converted by the solid state imaging device.
In such case, the frequency handled by the above mentioned driving circuit is so high that, in case such high capacity device as such solid state imaging device as a CCD is to be driven, it will be required to be driven at a particularly low impedance and therefore the generated heat amount will be large. Particularly, in an imaging apparatus in which the head part and the processing part processing a video signal are remotely connected with each other, the output buffer for transmitting the cable makes a low impedance conversion, that is, current amplification and therefore the generated heat amount is large. In most cases, this generated heat amount is larger than the generated heat amount by the solid imaging device. In such case, if the solid state imaging device and the substrate are filled with a resin or the like, the heat generated in the substrate will stay within the housing and will heat the solid state imaging device and, as a result, the S/N ratio will be reduced by the increase of a dark current and the heat generated noises will increase to be likely to deteriorate the picture quality.